1. Field of the Invention
The present invention relates to a light wavelength converting module, and in particular, to a light wavelength converting module which, by using a light wavelength converting element, converts the wavelength of a fundamental wave which is emitted from a semiconductor laser.
2. Description of the Related Art
Conventionally, in a case in which a semiconductor laser is optically coupled to a light wavelength converting element, and the wave, which exits from the light wavelength converting element and whose wavelength has been converted such as a second harmonic, is used as recording light of a light scanning/recording device such as a laser printer, in order to make the wave whose wavelength has been converted match a scanning optical system provided at the light scanning/recording device, the plane of polarization of the wave whose wavelength has been converted must be rotated by 90°.
In order to rotate by 90° the plane of polarization of the wave whose wavelength has been converted, a half-wave plate, which imparts an optical path difference of ½ of the wavelength to the two polarized light components which are orthogonal, is disposed at the exiting end surface side of the light wavelength converting element. The half-wave plate is formed from a white mica plate, a quartz crystal plate or the like which is birefringent. When the orientation of the long axis of the elliptically polarized light which is incident on the half-wave plate is θ from the main axis of the wavelength plate, the orientation of the long axis of the elliptically polarized light which exits from the half-wave plate is −θ. For example, if θ=45°, the elliptically polarized light incident on the half-wave plate and the elliptically polarized light exiting therefrom are orthogonal to one another. Namely, although the elliptical shapes of the polarized lights are the same, the directions of the long axes thereof are orthogonal to each other, and the directions of rotation of the polarized lights are inverted.
However, the wave whose wavelength has been converted and the fundamental wave whose wavelength has not been converted both exit from the exiting end surface of the light wavelength converting element. Further, the half-wave plate is disposed substantially orthogonal to the optical axis in order for the performances thereof to be exhibited as much as possible. When the half-wave plate is disposed at the exiting end surface side of the light wavelength converting element, a problem arises in that the fundamental wave is reflected by the half-wave plate, becomes so-called return light, again enters into the semiconductor laser, and becomes a source of noise.
Further, tilting the half-wave plate with respect to the optical axis such that the light reflected at the half-wave plate does not become return light, has been thought of in order to overcome the aforementioned problem. However, when the half-wave plate is inclined with respect to the optical axis, the performances of the half-wave plate cannot be sufficiently exhibited.